This invention relates to a running speed detecting device for marine vessels and more particularly to an improved, simplified and highly effective arrangement for indicating the speed of a watercraft that is accurate over a wide range of speeds.
There are a number of types of speed indicators employed for watercraft. These devices all operate on electrical principles and include either the propeller type wherein a propeller is mounted on the hull and rotates at a speed which will be related to the speed of the hull or of the magnetic current meter type. Such magnetic current meter type devices also are provided on the exterior of the hull and each system requires the provision of connecting wires for transmitting a signal from the sensor to a remotely positioned indicator. However, the accuracy of such devices depends on the effectiveness of the transmission of the electrical signal from the remotely positioned speed transducer to the speed indicator positioned in proximity to the watercraft operator. As a result, these devices tend to be inaccurate.
In order to improve the accuracy of watercraft speed indicators and in order to permit a device that can be used with a wide variety of watercraft, it has been proposed to utilize the water pressure as an indicator of speed. To this end, the hull is provided with a forwardly facing opening that receives the water pressure which will be dependent upon the speed of watercraft travel. A conduit then conveys the water pressure from the opening to a remotely positioned speed indicating device that incorporates a pressure transducer that outputs a signal indicative of water pressure. A converter circuit then converts this water pressure signal into a speed signal. An arrangement of this type is shown in the copending application entitled "Speedometer For Marine Vessels", Ser. No. 160,124, filed Feb. 25, 1988 in the name of Kazuhiro Nakahmma et al, which application is assigned to the assignees of this application.
Although the arrangement described in the aforenoted copending application is extremely effective in meeting its desired objects, still further improvement is possible. One difficulty with the type of device shown in that appliction is that at low speeds, the water pressure variation is such that it is difficult to obtain accurate speed readings. The reason for this is that at low speeds the pressure variation in response to speed variation is not that great and the difference in speed in relation to pressure does not offer the degree of resolution that is desirable for good performance.
It is, therefore, a principal object of this invention to provide a running speed detecting device for marine vessels that will provide an accurate signal of speed under a wide range of running conditions.
It is a further object of this invention to provide a running speed detecting device for a watercraft that will provide an accurate speed signal under all conditions.